Once, I dropped one of my journals into a puddle, and, because I used regular ink, irreplaceable sections just washed away.
Thought I was consigned to using ballpoint pens for my writing until I found Noodler's Eternal, bulletproof, and waterproof inks. I don't worry about losing stuff anymore, but I'd like to try different brands and colors, so long as they are waterproof.
Private Reserve has some eternal inks. Diamine has registrars ink which is iron gall based & permanent. R&K has iron gall inks- check out Peartreepens.com
MB might still make an iron gall blue/black but I can't be sure as they have changed around their inks.